I am recovering today from a misadventure. Yesterday, while cutting through the nearby park on my regular hill walk, I came across a curious sight: a whole pile of cute, fuzzy caterpillars on the sidewalk. Given their position, I thought they might have fallen from a webby nest overhead, but couldn’t find anything of the sort.
The caterpillars were having a hard time. This is a popular park among joggers and walkers, and very few of them watch where they put their feet. There was a lot of squishage.
Since I cannot walk away from critters in need, I set about rescuing the caterpillars that had survived. One by one, I picked them up and tossed them off the sidewalk, until about thirty of them were safely wandering about in the pine duff.
By Asqueladd, CC BY-SA 3.0, Link
About half an hour later, as I rounded the midpoint of my hill climb, I realized I’d been scratching my right hand without being aware of it. It had several raised welts.
I said, “Oh crap. Urticating hairs.”
There are several species of plants (think stinging nettles), spiders, and caterpillars that utilize urticating hairs as a defense mechanism. These are tiny, detachable hairs that deliver a toxin and cause itching and swelling in the victim, sometimes to the point of respiratory distress if the hairs have gotten into the nose or throat. I’m used to fuzzy woolly bear caterpillars from my home state; the idea of having to be careful of caterpillars here had not crossed my mind.
It occurred to me then that despite the appearance of sixty or so juicy caterpillars in an exposed, easily visible location, there had been no birds dining on this feast. I bet myself that when I walked back through the park, the squished ones would still be there.
They were. Obviously the Algarvean birds are far better informed than I was. (I’ve since learned that the great tit, Parus major, can eat them, but I didn’t hear any of those in the park yesterday.)
Upon returning home, I washed my hands thoroughly under cold water and found that actually made it worse. Then I hit the shower and oh yes, hot water helps. Temporarily.
The problem is that I had sweated on my hill climb, so I pushed up my sweatshirt sleeves and pulled my collar away from my neck. My hands had urticating hairs all over them, and they transfer easily. Result: I had a rash of raised welts all along my forearms and the back of my neck. Our bottle of Calamine lotion got a workout (it’s called Caladryl in Portugal).
A web search for “caterpillars + urticating + Portugal” procured an answer on the very first hit. They are pine processionary moth caterpillars, Thaumetopoea pityocampa, and wow are they nasty. Vets in the area know all about them, because dogs regularly get into these caterpillars with devastating results, including respiratory distress and death. Survivors sometimes have to have their tongues partially amputated.
Nor is the damage limited to dogs. Even without touching them, humans with heightened sensitivity can be affected when the wind blows loose hairs from caterpillar nests. Besides the skin rash and inflammation, respiratory issues can result without the victim having any idea of the cause.
The caterpillars themselves are really quite fascinating. They’re in the silk moth family, and live in silky “tents” they weave for themselves at the tips of pine branches. At night, they exit the nest to feed on pine needles, then return to the safety of their tent during the day.
By Chiswick Chap – Own work, CC BY-SA 3.0, Link
January through March is when they’re a real problem in Portugal. This is when they leave the nest permanently, march down the tree trunk, and look for soft soil to burrow into for their chrysalis stage. The spring migration is where the “processionary” part of their name comes into play, because they march head to tail, in a long, uninterrupted line.
Public Domain, Link
Woe betide any dog that sticks their nose into those. Or well-meaning humans who pick them up bare-handed.
At the end of the summer, the adult moths hatch out, and the females search for mates and a good-looking pine on which to lay their eggs. They have one day to accomplish their task. This means the range expansion is limited to how far an adult moth can fly in one day, but for all that, the pine processionary moth has a large range that encompasses much of southern Europe.
It appears that the toxins in urticating hairs get worse in a warm, humid environment, and I sleep hot. When I woke up this morning, my reaction had gotten far worse and is now doing a fair imitation of chicken pox. At this rate, I’m going to use up that bottle of Caladryl. I may be hitting the pharmacy tomorrow for a topical antihistamine.
At this point, I’m just grateful that I didn’t wipe the sweat out of my eyes on that walk. But at least I now know all about pine processionary caterpillars.
They’re still cute.